Method of qualification testing of DC-DC converters

Abstract

DC--DC power converters are an integral and critical component of telecommunications products. As a key component, the reliability of these devices has direct impact on quality of the products. Many of the converters utilized in telecommunications products are standard "off the shelf" commercial units, available from a wide variety of suppliers. With the recent proliferation of the use of these devices, former qualification methods had proven incapable of assuring the quality and reliability requirements for a telecom environment. Disclosed is the current setup, test, statistical analysis and failure analysis methods used to assess DC--DC power converter design quality and reliability.

What is claimed is: 
     
       1. A method of qualification testing of a group of DC--DC converters, comprising the steps of: (1) testing operation performance of all of the DC--DC converters in the group, under condition of normal temperature;   (2) testing thermal coefficients of expansion of a certain number of the DC--DC converters tested at step (1), upon application of thermal shock;   (3) testing functionality of a certain number of the DC--DC converters tested at step (2), upon application of power and thermal cycling;   (4) testing design margin of a certain number of the DC--DC converters tested at step (2), under step changes in temperature; and   (5) performing analysis using capability ratios to determine whether the failures of the group of the DC--DC converters are failed to be qualified, on the basis of short term and mid term capability ratios which are defined by upper and lower specification limits, mean and standard deviation.   
     
     
       2. The method of claim 1, further comprising the step of testing manufacturing flaws of a certain number of the DC--DC converters tested at step (2), under the conditions of biased humidity. 
     
     
       3. The method of claim 1, further comprising the step of testing the RF and/or audio emission of a certain number of the DC--DC converters tested at step (1). 
     
     
       4. The method of claim 1, further comprising the step of testing the short circuit protection of a certain number of the DC--DC converters tested at step (2). 
     
     
       5. The method of claim 1, wherein step (2) comprises the step of repeating air to air thermal shock at a specific number of cycles, the maximum and minimum test temperatures being specified. 
     
     
       6. The method of claim 1, wherein step (3) comprises the step of changing the test temperature at a specific ramp rate between specific minimum and maximum operating temperatures. 
     
     
       7. The method of claim 1, wherein step (4) comprises combined cycling of temperature, voltage, load and vibration. 
     
     
       8. The method of claim 1, wherein step (5) comprises the step of determining if the mid term capability ratio is less than a predetermined value, the group of the DC--DC converters will be failed. 
     
     
       9. The method of claim 8, wherein the predetermined value of the mid term capability ratio is 1.33, where the mid term capability ratio Cpk is given by:   Cpk=min (USL-μ/3σ), (μ-LSL/3σ)!     where, USL, LSL, μ and σ are the upper specification limit, the lower specification limit, the mean and the standard deviation, respectively.   
     
     
       10. A method of qualification testing of a group of DC--DC converters, comprising the steps of: (1) testing operation performance of all of the DC--DC converters the group, under the conditions of normal temperature;   (2) testing thermal coefficients of expansion of a certain number of the DC--DC converters tested at step (1), upon application of thermal shock;   (3) retesting thermal coefficients of expansion of a certain number of the DC--DC converters tested at step (2) at a specific number of cycling;   (4) testing functionality of a certain number of the DC--DC converters tested at step (2), upon application of power and thermal cycling;   (5) testing design margin of a certain number of the DC--DC converters tested at step (2), under step changes in temperature;   (6) testing manufacturing flaws of a certain number of the DC--DC converters tested at step (2), under the conditions of biased humidity;   (7) testing RF and/or audio emission of a certain number of the DC--DC converters tested at step (1);   (8) testing short circuit protection of a certain number of the DC--DC converters tested at step (2); and   (9) performing analysis using capability ratios to determine whether the failures of the group of the DC--DC converters are failed to be qualified, on the basis of short term and mid term capability ratios which are defined by upper and lower specification limits, mean and standard deviation.   
     
     
       11. The method of claim 10, wherein step (9) comprises the step of determining if the mid term capability ratio is less than a predetermined value, the group of the DC--DC converters will be failed. 
     
     
       12. The method of claim 11, wherein the predetermined value of the mid term capability ratio is 1.33, where the mid term capability ratio Cpk is given by:   Cpk=min (USL-μ/3σ), (μ-LSL/3σ)!     where, USL, LSL, μ and σ are the upper specification limit, the lower specification limit, the mean and the standard deviation, respectively.